Hard floor surfaces in commercial and institutional establishments including restaurants, commercial kitchens, hospitals, laboratories and retail stores often become relatively slippery after use and repeated cleanings, leading to slip and fall injuries. Both employees and customers can be injured in slips and falls resulting in significant expense for medical attention, Workers' Compensation costs, lost time and liability-associated costs, such as insurance premiums, compensatory awards and/or settlement costs. In the food industry, slip and fall injuries to employees can also include indirect injuries such as when the employee touches a hot surface while attempting to arrest a fall and is burned.
Hard floor surfaces, when clean and new, have an inherent coefficient of friction (COF) characteristic of the surface material. The COF is generally defined as the amount of force parallel to a surface that is required to move or make slip a force or weight that is normal to the surface, divided by the weight. Rougher surfaces generally have a higher COF whereas smoother surfaces have a lower COF.
COF can be measured using the American Society for Testing and Materials (ASTM) Test C 1028-89. This test is the U.S. ceramic tile industry's standard test for assessing the slip resistance of ceramic tile and other like surfaces. The test is used to measure the frictional force between a flooring surface and a slider made of laboratory grade Neolite, a synthetic rubber. The test result can be expressed as a static COF. The term static is used because the two surfaces are at rest with respect to each other when the test is made.
The slider used in ASTM C 1028-89 is three inches square. The slider is first calibrated using a standard reference tile. The slider is then placed on the sample flooring surface and a 50 pound weight is placed on the slider. A dynamometer which measures force in pounds is used to pull the weighted slider to initiate a small movement across the flooring. This pulling force is then divided by the weight on the slider and the result, after correction using the slider calibration data, is equal to the static coefficient of friction.
The flooring can be tested both dry and wet with water. In each case, the COF is measured twelve times and the results are averaged. The ASTM test method specifies that each flooring sample should consist of three pieces of the tile. For each of the three pieces, a pull is made in each of four directions, e.g. north-east-south-west.
According to the Ceramic Tile Institute, a COF of greater than 0.6 is considered safe; a COF of between 0.5 to 0.6 is conditionally acceptable; and a COF less than 0.5 is considered unsafe.
The COF can be increased by the presence of macroscopic and microscopic variations in the surface. Macroscopically, a floor may include a pattern visible to the naked eye such as on tiles or in a terrazzo floor surface. Microscopically (e.g., when viewed at about a 450X magnification), a new clean floor material typically has a non-smooth surface made up of peaks and valleys and a pore structure which present a shoe-gripping surface. Some hard surfaces, such as those on polished marble and granite, terrazzo and smooth ceramic tiles have a relatively low COF and therefore are generally more slippery. Other surfaces typically used in commercial flooring including grouted quarry tile or cementitious concrete have a rougher surface texture resulting in a higher COF and a less slippery surface.
The COF of a hard surface can be altered over time by accumulation of fats and oils (collectively known as grease), accumulation of spilled food materials or other dirt, accumulation of cleaning residues especially from alkaline cleaning solutions, deposition of minerals from the water supply (water hardness), grout joint saponification or any combination of these factors. These accumulations generally fill the peaks and valleys and the pore structure of the surface making it smoother and lowering the COF. In commercial kitchens and restaurants, polymerization of fats and oils producing a hard, dense, greasy film is particularly responsible for increased slipperiness. Polymerized grease can reduce the COF of a floor surface about 50% in less than 30 days leading to an increased probability of slipping and falling by employees and patrons. Also, abrasion resulting from normal pedestrian traffic can lower the COF by polishing the surface over time. Abrasion polishing occurs especially on unglazed quarry tile surfaces.
Research in pedestrian safety has shown that the surface total mean peak-to-valley roughness (Rtm) is a good indicator of traction on surfaces wetted by water. The instrument used in this research is the Taylor Hobson Surtronic 10. The instrument has a sylus of radius of approximately 7 .mu.m. The stylus traverses a path of 0.8 mm and measures the height difference between the lowest valley and the highest peak. Five such paths are evaluated and the results electronically averaged for each reading on the instrument. Roughness can then be expressed as the average maximum peak-to-valley height difference in .mu.m. For reference, the approximate Rtm of some common materials is shown below in Table 1.
TABLE 1 ______________________________________ Material Rtm (.mu.m) ______________________________________ Clear glass 0.1 Picture frame non-glare glass 3 Silicon carbide sandpaper: 1500 grit (extremely fine) 13 400 grit (super fine) 30 320 grit (extra fine) 46 ______________________________________
Cleaning of hard surface floors to remove accumulated deposits and restore the COF to that of the clean new surface can be accomplished in a number ways. Scrubbing or mopping with a cleaning solution that contains an alkaline emulsifier can temporarily restore a floor surface but often leaves a residue of soap scum which can itself build up and eventually fill the peaks and valleys and a pore structure of the surface. Alkaline cleaning solutions can also precipitate silicon and calcium in the water supply resulting in accumulation of mineral deposits, thus reducing the COF despite the removal of grease film. Scrubbing with a deck brush and hot water (67.degree. C./160.degree. F.) followed by vacuuming of the wet surface ("wet vac") or squeegee removal of the solution containing the suspended dirt particles before thorough rinsing is effective at cleaning off grease film but requires expensive equipment and significant training of personnel in the use of the equipment.
Some of the types of the currently available cleaners include slip resistance packet cleaners (e.g., SAFETY-TRAC.RTM. by Kay Chemicals); powder alkaline cleaners (e.g., TIDE.RTM. by Colgate Palmolive); degreasers (e.g., RECOVER.RTM. by Dubois); sodium hypochlorite solutions (e.g., CLOROX.RTM.); alkaline-based steam cleaners (e.g., STEAM CLEANERS.RTM. by Union Carbide); and acid-based cleaners (e.g., DRACKET SURE-TRAC.RTM. by Bristol Meyers, SAFETY STEP.RTM. by Dynamic Research, and the cleaner disclosed in U.S. Pat. No. 5,223,168 issued to Holt). A number of additional liquid alkaline cleaners are available, such as REGAIN and MAXICLEAN by Ecolabs, POWERFOAM by SSDC Corporation and TITAN by Kay Chemical. However, all of the foregoing products suffer from a variety of drawbacks. Many of these products contain hazardous concentrations of chemicals, and therefore, require special care in use. Additionally, some of these products require multiple steps during their use (e.g., separate cleaning, restoring and neutralizing steps) or specialized equipment (e.g., steamer equipment). Moreover, most of these products are limited to a single use, and multiple products are required in order to adequately maintain a floor.
In addition to cleaning of the floor surface of accumulated grease, soil, mineral deposits and soap scum, restoration of the surface pore structure and peaks and valleys is important in improving floor texture, especially in areas of pedestrian traffic. Areas of pedestrian traffic include those in which employees and/or customers regularly walk during normal hours of operation of the commercial establishment. Restoration of surface irregularities has been accomplished by acid or mechanical etching (e.g., grit blasting) of floor surfaces. However, both processes have been found unsatisfactory because of exposure of personnel to highly acidic compounds, invasiveness of the cleaning procedure to normal commercial operations, and costs, particularly if a specialty contractor performs the procedure. Also, such etching procedures eventually weaken the floor tile surface. In addition, highly acidic solutions are subject to significant governmental regulation relating to health and safety during their use and transportation (i.e., those under OSHA and the Department of Transportation).
Surfaces that contain silicone dioxide components such as quarry tile have been treated with acidic solutions to etch the surface and thus restore a roughness to the floor. Treatments containing ammonium fluoride and hydrofluoric acid have long been known as agents for etching silicon substrates such as in the etching and frosting of glass or the treatment of silicone "chips" for computer components as disclosed by Scardera et al. in U.S. Pat. No. 4,761,245 and Ohmi et al. in U.S. Pat. No. 4,795,582.
Commercially available hydrofluoric acid treatment solutions have a pH in the range from about 0.1 to about 2.4. Treatment of quarry tile with these highly acidic solutions requires multiple steps. After the surface is treated with the acidic solution, it must be neutralized (usually with extensive rinsing) and dried. The highly acidic treatment increases the COF but also results in deep pitting and undercutting to produce sharp platelets in the tile surface. The deep pits can collect fats, oils, and dirt, thus decreasing the COF over time. The sharp undercut platelets can cut mop strings thus damaging cleaning equipment and leading to accumulation of lint. The platelets rapidly wear down in areas of pedestrian traffic and thus result in repolishing of those surfaces where maintaining a relatively high COF is most important.
The Americans with Disabilities Act (ADA) requires that areas accessible to disabled persons be slip-resistant. The U.S. Department of Justice's Access Board, which administers parts of ADA, in its Bulletin No. 4 recommends a minimum average static COF of 0.60 for level floors and 0.80 for ramps. This standard is also recommended by various other governmental and nongovernmental authorities, including the Ceramic Tile Institute and the City of Los Angeles. Not only must the initial flooring material meet these requirements, but, the requirements for COF must also be met on an ongoing basis.
Hence, there is a need for a method of restoring floor surfaces in commercial and/or institutional establishments that both cleans and restores the uneven surface of the floor in a manner that can be performed easily and safely by employees of the establishment with a minimum of training and equipment. There is a need for a method that restores a floor's COF without causing deep pitting or undercut platelet formation. Furthermore, there is a need for a method that employs chemical solutions that can be easily transported and safely used with standard levels of care (e.g., protective gloves and eye protection) without exposing personnel to highly acidic or alkaline solutions or toxic fumes.